History
Visual Effects has perhaps one of the most amazing pasts of any industry, and perhaps the least known. Go to a College or University for amost any other industry, and you'll find them teaching the history of it. For a project I did in the Advanced Television and Film program at Sheridan College, I did an informal survey of about 50 visual effects artists. Not one of them knew who George Méliès, the father of Visual Effects was. For that program, I wrote a paper on George Méliès, you can read it here.
The revolution really kicked in around 1976 or so. Industrial Light and Magic formed to create the groundbreaking work on "Star Wars: A New Hope." They pioneered the techniques of motion control photography, a type of camera crane that can repeat camera moves accurate to the frame, over and over again to get different layers. Those layers were eventually combined on a machine called an optical printer. An optical printer is basically a film projector pointed at a film camera. More sophisticated printers project one film's image to a focal plane, in which is another piece of film. Called Arial printers, they create a virtual image in the place occupied by another piece of film. These are usually used for travelling matte photography.
Travelling mattes are used to combine (or composite) a live-action foreground, usually photographed in front of a blue-screen with a background shot at a different time. This can place actors in a different location, or even in a location that doesn't exist. The forground, actors or a model, are filmed in front of a flat blue screen. The blue screen will later be replace by the new background. This foreground element is rephotographed in an optical printer, onto film which is only sensitive to blue light. This film is also very high contrast, and is therefore named High-Con film. What results is a new film, showing a silhouette of the foreground action. It's opposite is created by rephotographing it to create it's negative image, these two opposite silhouettes of the forground image are called mattes. The foreground element, the two mattes, and the background element are now used to create the final composite image.
The process usually begins by projecting the background image through the forground hold-out matte. This allows the background image through, except where the black silhouette of the foreground holds-out the background. What results is an image on the new film of the background with a hole where the forground will be put. The new film is then rewound, and re-exposed, this time to the foreground image through the opposite matte. This exposes the foreground in the hole left by the last run. The matte prevents the blue screen from being exposed on the new film.
This process effectively replaces the blue screen with a new background. The process is called compositing, and has been entirely replaced by digital techniqes. The film elements are now scanned into digital files, and a computer is used to replace the blue or green screen with a new background. While it used to be neccesary to physically create whatever was to be seen, and film it with a camera, it is now possible to create images entirely with a computer. The process of CGI, or Computer Generated Imagery consists of creating a digital model, "painting" or otherwise texturing the model and programming the model's movements. An artificial camera can now shoot a digital scene, with synthetic lighting. This techniqe was first used to create a digital character when a stained glass window comes to life in "Young Sherlock Homes." Techniqes of CGI were refined at a tremendous pace for the digital dinosaurs of Jurassic Park, and have even created digital humans for "Final Fantasy."
Digital Visual effects hold great promise, and will continue to be refined and new techniqes created. A combination of digital and photography was used for the "bullet time" effects in "The Matrix." A set of still cameras took images at the same time, or in sequence so that the virtual camera could move while time stood still. The backgrounds for these sequences were generated by computer, and computers were used to create the frames in between still camera locations, a process called interpolation which I've done to fix film splices.
Here's some links to web resources for visual effects:
VFX Pro - used to have a library
of articles about the visual effects in movies, but after being swollowed
by a larger company it now has just current news.
Cinefex - THE industry journal. Unfortunately the site is just a big ad for the magazine, but they do have a few sample articles online, including E.T.
The
Art and Science of Special Effects - neat little page of stuff.